Adaptive braking system false trigger hold-off circuit



Dec. 1, 1970 D. w. HOWARD ETAL 3,544,172

SYSTEM FALSE TRIGGER HOLD-OFF CIRCUIT ADAPTIVE BRAKING Filed Dec. 16, 1968 xw mm w 3% 5 3258 m mmnwwwmn. 52mm 40528 ow m\ mo Q Q 6% $20 E a 1W0 L I Q & k

00mm w Hon m0 THOMAS-C. SGHAFER INVENTORS ORNEY United States Patent Oifice Patented Dec. 1, 1970 3,544,172 ADAPTIVE BRAKING SYSTEM FALSE TRIGGER HOLD-OFF CIRCUIT Donald W. Howard and Thomas C. Schafer, South Bend,

Ind., assignors to The Bendix Corporation, a corporation of Delaware Filed Dec. 16, 1968, Ser. No. 783,813 Int. Cl. B60t 8/08 US. Cl. 303-21 8 Claims ABSTRACT OF THE DISCLOSURE An improved control channel for an automobile adaptive braking system wherein control signals which are generated after a controlled wheel decelerates to a predetermined reference are applied to a braking pressure controller to automatically control the braking pressure applied to the controlled wheel so as to optimize wheel braking characteristics. An acceleration switch senses wheel or axle vertical acceleration forces and in response thereto causes one or the other of a pair of one-shots to generate an output pulse which inhibits a gate through which the control channel control signal must pass on its way to the brake pressure controller, thus preventing vertical acceleration forces (false triggers) from activating the brake pressure controller.

CROSS REFERENCES TO RELATED APPLICATIONS The false trigger hold-off circuit disclosed herein is an improvement for automobile, truck and the like adaptive braking systems of the type disclosed in a patent application for Automobile Anti-Skid Control System, by M. Slavin et al., application Ser. No. 712,672 filed Mar. 13, 1968 and which is assigned to the assignee in the present application. The prior application is specifically referred to below and hereby incorporated by reference.

BACKGROUND OF THE INVENTION This invention relates to improvements in automobile braking systems and more particularly to improvements in adaptive braking systems which initiate a control signal in response to an initial wheel deceleration signal or other suitable wheel signal.

There was described in the aforementioned patent application Ser. No. 712,672 an adaptive braking system control channel which includes a sensor mounted on a vehicle wheel which generates pulses at a rate proportional to wheel rotational speed. These pulses are accumulated in a counter so as to generate a DC. voltage level proportional to wheel rotational speed, with this latter signal being difierentiated to provide an electrical signal proportional to wheel acceleration and deceleration. The deceleration signal is compared in a comparator against a reference deceleration level so as to generate an error signal whenever the wheel deceleration attains the reference deceleration. The error signal activates a memory which memorizes the instantaneous wheel speed .over a predetermined short time period. -If during this time period wheel speed drops by a predetermined percenta'ge a control signal is allowed to pass through a gate qualified by a signal from the vehicle brake switch, to

a brake pressure controller, which in response thereto acts to attenuate the braking pressure at the controlled wheel. When bra-king on a rough surface, however, such as at a railroad crossing, at a deceleration level below the threshold of adaptive braking action, the braking pressure controller can be activated even though brake pressure is relatively low. This is caused as follows. When the wheels bounce in a vertical plane, often leaving the road surface, the frictional coefiicient which tends to keep the braked wheel rotating when the wheel is in contact with the road surface now drops to zero or a very low value and wheel speed rapidly decreases, thus possibly providing the necessary elements for triggering the brake control system. In order to allow the brake control system to distinguish between such a false alarm and a proper initiating signal, it is neecssary to provide an inhibit or hold-01f signal of a predetermined time period if the initiating signal is caused by forces which tend to urge the wheel from the road surface, in other words, vertical acceleration forces.

SUMMARY OF THE INVENTION Accordingly, an improvement to known adaptive braking systems has been devised comprising a false trigger hold-off circuit. An acceleration switch which will open in response to acceleration forces applied along its active axis is mounted in the vehicle with its active axis vertical, suitably on the wheel or vehicle axle whose braking characteristics are to be controlled by the control channel. The acceleration switch is thus sensitive to vertical acceleration impulses such as would be caused by the wheel passing over railroad crossings, chuck holes or other road imperfections. Opening of the acceleration switch causes one or the other of a pair of one-shots, only one of which is energized, to generate an output pulse which is applied to inhibit an AND gate through which the control channel control signal must pass on its way to a brake pressure controller. The one-shot output pulse is also used to toggle a flip-flop which in turn deenergizes the one-shot and energizes the other one-shot. The use of the dual one-shots, only one of which is energized at a time, eliminates the dead spot oecuring during the one-shot reset time. This allows the system to provide a continuous hold-off capability if the vertical acceleration pulses appear on a repetitive basis at a rapid rate. An object of the present invention is thus to provide a means for preventing false triggers from affecting the operation of an adaptive braking control channel.

Another object of this invention is to provide a means of the type described which is compatible with known existing adaptive braking systems.

hTese and othe robjects of this invention will become apparent to one skilled in the art upon a reading and understanding of the following disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS The figure is a block diagram of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the figure, there is seen an adaptive braking control channel 20 and the elements of the invention as they would be installed on an automobile, truck, or the ke-.As 19 as brake. S it h .24, wh h .i ..gang t then. 1eve1. an,,d,the .wheelspeedthen decreases.bynarpredetere. vehicle brake pedal, is open, that is when the brake pedal mined percentage within a predetermined time period. is not depressed, gate 25 is inhibited by an A+ voltage Where this type of control channel is used it is necessary acting through the voltage divider comprised of resistors that the period of the one-shot be at least equal to the 21 and 22, Thus, during this tiine any control channel predetermined time period during which the control chan- 20 control signals which might be generated along line nel can be activated. At the completionof thepne-shot 20a are blocked from passing through to the brake presoutput pulse the .voltage-transit'ions'i's' inyertedi byxinverter sure controller '26. It now, the brake pedal is depressed 18 to trigger flip flop'-'1-7 into, forfthisf'example, the'l'reset so that switch 24 closes, the gate 25inhibiting signal on state so that fiip-flop reest output line -'17b-and-orie shot line 24a is extinguished. If at the same time there is no 1 16 are now-energize" It is thus possibl' t'o' ontin gate 25 inhibiting signal on line 19a, such as would be the hold gate 25 inhibitedjif thef" puti- -p ul case as long as acceleration switch remains closed, in a leration switch10' occur at manner" to' be described below, "control signals generated rapid rate.- 1; i

by control .channel 20 will pass along line 20a and While we have taughtwhatwe. ave.conmderedtmbeithrough gate 25 to the brake pressure controller 26 to the preferred embodiment-ofcur-invention, it is obvious thus initiate control of the braking pressure on the wheel that certain changes and modifications can be made by or wheels controlled by control channel 20. As has been one skilled in the art without departing from our inve'npreviously explained for certain known types of control tion. We therefore claimas our invention all such changes channel the output control signal is generated only after and modifications which fall within the true scope and wheel rotational deceleration exceeds a predetermined spirit of the appended clainisi reference deceleration level. For other known types of The invention claimed control channel, such as that described in the aforemen- 1 In a wheeled Whidehaving a wheel kin systemv tioned patent application Ser. N0. 712,67 the 60111101 whereby said vehicle wheels are braked by a-braking force. Signal is generated y after the Controlled Wheel attains to decelerate said wheels and including an adaptive brak .the reference deceleration level and additionally thereing control channel gene rafing a control signal and aftcf drops in Speed by a predetermined percentagewitha brake pressure controller responsive to said control in a predetermined time period. As long as the controlled signal for controlling saidbraking-force on at least one wheel remains in contact with the road surface these conof said wheels, saidzcontrol channel being triggered by.- ditions for the generation of the control signal will be an electrical signal proportional to rotationaldeceleraattained only when locking of the controlled Wheel be- 30 tion of one of said controlledwheels, amimproyementeto comes imminent. If, during a braked stop, where the comsaid control channel, to. prevent false triggering of said bination of braking pressure and tire to road surface concontrol channel comprising:

, 1 ditions are such that the conditions necessary to cause accelerometer means-responsive to;-verticalacceleration. control channel 20 to generate a control signal are not forces on at least one of said controlled wheels-for present, the wheel is suddenly forced to leave the road generating an inhibiting; signal;;;-and,-- surface such as by striking a chuck hole, the sudden means responsive to said inhibiting signal for inhibiting.- release of tire to road surface friction will cause the said control signal. i I wheel to rapidly and abnormally decelerate thus possibly 2. An improvement-to said, control channel asrecited= triggering control channel 20 .to generate the control in claim 1 wherein said acceleration meanscomprises; signal. If this control signal could now pass directly into 40 an accelerometer responsive;to-.-ventical acceleration;- the brake pressure controller 26 the braking pressure of forces on at least oneof said controlled wheels for,- the wheel would be released so that upon the wheel subgenerating a vertical. acceleration signal; sequently coming into'contact with the road surface the timed means triggered by said vertical acceleration braking capacity of the wheel would be greatly diminsignal for generating an outputpulse having a preished. It is thus necessary that the force which impelled determined time period, said output pulse comprising the wheel to leave the road surface must also cause a said inhibiting signal.

gate inhibiting signal to appear on line 19a to thus rare '3. An improvement to said control channel as recited vent the control channel control signals from reaching the in claim 2 wherein said inhibiting means comprises a gate brake pressure controller 26 underthese conditions. This means Connecting said'i control Signal n Said ak is accomplished as follows. A nomally closed accelera- Pressure Controller, i gate nsy said" tion switch 10, having an active axis, that is an axis along b t g S gna which acceelration forces must be applied to cause the 4. An improvement to said'control:-channel-aswecited" switch to open, is mounted on the vehicle wheel or axle in claim 3 wherein said timed means comprises a one-shot with its active axis vertical. The dual one-shots 14 and 16' triggered by said vertical acceleration signal for generahave their trigger inputs normally grounded through 5 ting a one-shot output-pulswsa d one-shot output-pulse' switch 10. It will be further not that the one-shots '14 comprising said inhibiting signal.

and 16 receive power and are energized by the flip-flop 17 An improvement 1 said .control.:channel'-as'recited output set and reset lines 17a and 17b, respectively, so in claim 2 wherein said timed meansc'omprise's: that only one of the one-shots may beenergizedat a. time. means triggered by saidyertical acceleration signal depending on whether the flip-fiop is in the set or reset whenenel'giled for generating a aoutput' pulse;.; state. Assuming now that flip-flop If! is initially in-the set second I meansv triggered by-.,s a;id: vertical-acceleration state so that output line 17a and hence one-shot 14 are sig alwhen energizedifor g n. energized and that during a braked stop the, wheel on PM 1 36; which acceleration switch 10 is mounted hits a chuck hole with such force that switch 10 opens. One-shot 14 will thus be triggered by the A+ voltage acting. through the voltage divider comprised of resistors 11 and 12. The I, oneshot output pulse is applied through OR gate 19 and. said inhibitin'g signal along line 19a to an inhibiting terminal of gate 25, thus 6. Animproven'1e'nt to. v ,ch preventing any control signals which might be generated: in claim 5 wherein saidenerglzing meansycoinprises: on line 20a from reaching brake pressure controller 26. gating means for passing;'both,. saidafirst;and.second, It will be remembered that in describing the control chan output pulses, said passedpulse comprising. .said. nel it was mentioned that one type of control channel inhibiting signah-nnd generates a control signal only after the wheel decelerabistable meanstriggere vymsaid inhibiting ignal for}: tion has exceeded a predetermined deceleration reference alternately energizing-saidg first and secondgmea'ns.

5 7. An improvement to said control channel as recited in claim 6 wherein said first and second means comprised first and second one-shots respectively.

8. An improvement to said control channel as recited in claim -6 wherein said bistable means comprises:

a bistable element for alternately energizing said first a and second means; and, means responsive to the trailing edge of said inhibiting signal for triggering said bistable element.

6 References Cited UNITED STATES PATENTS 1/1968 Marcheron 30321(A4) 9/1968 Williams et a1. 30321(A4) US. Cl. X.R. 3 03-20 

